prune-trace: list available pruners

By using the AliasedRegistry, "prune-trace --help" (and
"prune-trace -p '?'") now lists all available Pruners to the user.

Change-Id: Ib5e3d00aabc37e6d48d804d2d709812af3f7efb2

tools/prune-trace/Pruner.hpp

@@ -4,8 +4,9 @@
 #include <vector>
 #include <string>
 #include "util/Database.hpp"
+#include "util/AliasedRegisterable.hpp"
 
-class Pruner {
+class Pruner : public fail::AliasedRegisterable {
 protected:
 	int m_method_id;
 	fail::Database *db;